Interlocking socket base for an integrated circuit package

ABSTRACT

A socket for an electronic assembly. The socket may include a first finger that is coupled to a second finger. The socket may further have a plurality of contacts that are located within contact openings of the first and second fingers. The fingers may be separated by spaces that reduce the effective coefficient of thermal expansion.

BACKGROUND OF THE INVENTION

[0001] 1. FIELD OF THE INVENTION

[0002] The present invention relates to a socket that can be attached toa motherboard and be mated with an integrated circuit package.

[0003] 2. BACKGROUND INFORMATION

[0004] Integrated circuits are typically assembled into packages thatare mounted to a printed circuit board. The printed circuit board may bea motherboard of a computer. The integrated circuit package can beplugged into a socket mounted to the motherboard. The socket typicallyhas a plurality of contacts that are soldered to the motherboard andwhich can receive corresponding pins of the integrated circuit package.The socket contacts may be solder balls that are soldered tocorresponding surface pads of the motherboard. Surface mount solder ballinterconnects are preferred when integrated circuit packages are to besoldered to both sides of the motherboard. Additionally, surfacemounting increases the routing density of the board. The integratedcircuit package is plugged into the motherboard by inserting the pins ofthe package into the contacts of the socket.

[0005] The contacts are integrated into a dielectric base of the socket.The base is typically constructed from a molded fiber filled resinmaterial. The fibers typically become aligned in the direction of flowduring the molding process. The resultant socket may have a nonuniformcoefficient of thermal expansion (“CTE”). For example, when a liquidcrystal polymer (“LCP”) resin is employed the socket may have a CTE of10-15 parts per million per degrees centigrade (“ppm/° C.”) in thedirection that the fibers are oriented, and a CTE of 50-60 ppm/° C. in adirection normal to the fiber orientation. The motherboard may beconstructed from a material that has a CTE of 15-17 ppm/° C. Variationsin temperature will cause the socket to expand/contract at a differentrate than the motherboard particularly in the direction normal to thefiber orientation. The differential expansion may cause failures at thesolder joints of the motherboard and socket contacts.

[0006] Some sockets contain a mineral filler to minimize the CTE in thecross flow direction. The mineral filler is difficult to mold andincreases the cost of producing the socket. There have also beenattempts at integrating stress relief holes in the socket, but such asolution reduces the structural integrity of the part. It would bedesirable to reduce the thermal expansion of an integrated circuitsocket in the direction normal to fiber orientation withoutsignificantly increasing the cost or reducing the structural integrityof the socket.

[0007] The socket is typically molded by injecting the resin through agate. The resin will typically flow from the gate in a radial manner.The radial flow creates a nonuniform CTE throughout the socket. It wouldbe desirable to provide a socket that will increase the uniformity andpredictability of the CTE throughout the socket.

SUMMARY OF THE INVENTION

[0008] One embodiment of the present invention is a socket for anelectronic assembly. The socket may include a first finger that iscoupled to a second finger. The socket may further have a plurality ofcontacts that are coupled to the first and second fingers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a perspective view of an embodiment of an electronicassembly of the present invention;

[0010]FIG. 2 is an exploded view of a socket of the assembly;

[0011]FIG. 3 is an enlarged perspective view showing a plurality offingers of the socket;

[0012]FIG. 4 is an enlarged top view showing spaces between adjacentfingers;

[0013]FIG. 5 is a top view showing a finger being molded.

DETAILED DESCRIPTION

[0014] Referring to the drawings more particularly by reference numbers,FIG. 1 shows an embodiment of an electronic assembly 10 of the presentinvention. The assembly 10 may include a socket 12 that is mounted to aprinted circuit board 14. The printed circuit board 14 may be themotherboard of a computer system. The socket 12 may be mounted to thecircuit board 14 by solder balls (not shown) that are reflowed ontocorresponding surface pads 15 of the board 14. The solder balls may bearranged in a ball grid array (BGA) pattern.

[0015] An integrated circuit package 16 may be plugged into the socket12 and coupled to the printed circuit board 14. The package 16 maycontain an integrated circuit (not shown) that is electrically connectedto a plurality of external pins 18. The pins 18 can be inserted into thesocket 12 to connect the integrated circuit to the printed circuit board14.

[0016] As shown in FIGS. 2 and 3, the socket 12 may include a substrate20 which has a plurality of first fingers 22 that extend from a firstbase 24 and a plurality of second fingers 26 that extend from a secondbase 28. Each finger 22 and 26 may contain a plurality of contacts 30that are located within contact openings 32. The contacts 30 are adaptedto receive the pins 18 of the integrated circuit package 16 shown inFIG. 1. The contacts 30 may be connected to the solder balls that aresoldered to the printed circuit board 14.

[0017] Each first finger 22 may have a plurality of protruded areas 34that form a slot 36. Each first finger 22 may have a slot 36 on eachside of the finger 22. The slots 36 receive a corresponding tongue 38formed in the second fingers 26 to interlock the fingers 22 and 26. Thetongues 26 and outer protruded areas 34 may each have chamfered surfaces40 that lead the second fingers 26 into the first fingers 22. Thefingers 22 and 26 can be formed from a molded fiber filled resinmaterial. By way of example, the molded fiber filled resin material maybe a fiberglass filled liquid crystal polymer (“LCP”). The fingers 22and 26 may be molded or liquid crystal styrene (“LSC”) so that thefibers are oriented in a direction that is essentially parallel with alongitudinal axis 42 of each finger 22 and 26. The coefficient ofthermal expansion (“CTE”) of the fingers along the longitudinal axis 42is typically lower than the CTE normal to the axis 42. The CTE along thelongitudinal axis approximates FR4 motherboard material.

[0018] Separating the socket substrate 20 into separate fingers 22 and26 decreases the effective thermal expansion of the socket 12. It beingunderstood that the amount of thermal expansion of the socket is afunction of the expansion of each finger 22 and 26 pursuant to theequation:${\Delta \quad L} = {{\alpha\Delta}\quad {T \cdot \frac{W}{2}}}$

[0019] where;

[0020] α=the coefficient of thermal expansion;

[0021] ΔT=the change in temperature;

[0022] W=the width of a finger.

[0023] The thermal expansion of each finger 22 or 26 is about the centerline of the finger 22 or 26. As shown in FIG. 4, the socket 12 may beconstructed so that there are spaces 44 between the fingers 22 and 26.The spaces 44 allow adjacent fingers 22 and 26 to thermally expand, asindicated in phantom, without displacing the adjacent finger 22 or 26.Segmenting the socket into separate fingers may reduce or eliminateloads generated by the thermal expansion of the socket 12 relative to anon-segmented socket depending upon the temperature differential and thespaces between the fingers 22 and 26. The effective coefficient ofthermal expansion in the direction normal to fiber orientation may bereduced to more closely approximate the CTE of the circuit board 14.Matching the CTE's of the circuit board 14 and socket 12 may reduce thestresses within the solder balls mounted to the board 14.

[0024] Referring to FIG. 2, the first base 24 may have a plurality ofapertures 46 that receive corresponding protrusions 48 of the secondbase 28. The protrusions 48 may have an interference fit with theapertures 46 that prevents longitudinal movement of the fingers 22 and26 when the socket 12 is assembled. The first base 24 and fingers 22 canbe fastened to the second base 28 and fingers 26 with an adhesive,fasteners, or any other means.

[0025]FIG. 5 shows the fingers 22 or 26 being formed with an injectionmold process. The fiber filled resin 50 may flow into a mold 52 in adirection essentially parallel with the longitudinal axis 42 of theresultant fingers 22 or 26. The fibers 50 will orient in the directionof resin flow. The socket will have a CTE along the longitudinal axis,and an effective CTE normal to the longitudinal axis, thereby providinga socket that has only two expansion directions. The present inventionthus provides a process which increases the likelihood that the fibersare oriented in one direction and minimizes the thermal expansion of theresultant socket in a direction normal to fiber orientation.

[0026] While certain exemplary embodiments have been described and shownin the accompanying drawings, it is to be understood that suchembodiments are merely illustrative of and not restrictive on the broadinvention, and that this invention not be limited to the specificconstructions and arrangements shown and described, since various othermodifications may occur to those ordinarily skilled in the art, such ashaving multiple rows of contacts per finger.

What is claimed is:
 1. A socket for an electronic assembly, comprising:a first finger; a second finger that is coupled to said first finger;and, a plurality of contacts that are coupled to said first and secondfingers.
 2. The socket of claim 1 , wherein said first finger has a slotthat receives a tongue of said second finger.
 3. The socket of claim 1 ,wherein said first and second fingers each have a longitudinal axis andcontain fibers that are oriented essentially parallel with thelongitudinal axis.
 4. The socket of claim 1 , wherein said first fingeris separated from said second finger by a space.
 5. The socket of claim1 , wherein said first finger extends from a first base and said secondfinger extends from a second base, said first base having an aperturethat receives a protrusion of said second base.
 6. A socket for anelectronic assembly, comprising: a first base; a first finger thatextends from said first base; a second base; a second finger thatextends from said second base and is interlocked with said first finger,said second finger being separated from said first finger by a space;and, a plurality of contacts that are coupled to said first and secondfingers.
 7. The socket of claim 6 , wherein said first finger has a slotthat receives a tongue of said second finger.
 8. The socket of claim 6 ,wherein said first and second fingers each have a longitudinal axis andcontain fibers that are oriented essentially parallel with thelongitudinal axis.
 9. The socket of claim 6 , wherein said contacts arelocated within contact openings of said first and second fingers. 10.The socket of claim 6 , wherein said first base has an aperture thatreceives an insert of said second base.
 11. An electronic assembly,comprising: a printed circuit board; a socket mounted to said printedcircuit board, said socket having a first finger that is coupled to asecond finger and a plurality of contacts attached to said first andsecond fingers; an integrated circuit package that has a plurality ofcontacts that are coupled to said contacts of said first and secondfingers.
 12. The assembly of claim 11 , wherein said integrated circuitpackage contacts include a plurality of pins.
 13. The assembly of claim11 , wherein said first finger has a slot that receives a tongue of saidsecond finger.
 14. The assembly of claim 11 , wherein said first andsecond fingers each have a longitudinal axis and contain fibers that areoriented essentially parallel with the longitudinal axis.
 15. Theassembly of claim 11 , wherein said first finger is separated from saidsecond finger by a space.
 16. The assembly of claim 11 , wherein saidfirst finger extends from a first base and said second finger extendsfrom a second base, said first base having an aperture that receives aprotrusion of said second base.
 17. A method for forming a socket for anelectronic assembly, comprising: molding a first finger with a fiberfilled resin wherein a fiber is oriented essentially parallel with alongitudinal axis of the first finger; molding a second finger with thefiber filled resin wherein the fiber is oriented essentially parallelwith a longitudinal axis of the second finger; and, coupling the firstfinger to the second finger.
 18. The method of claim 17 , furthercomprising the step of attaching a plurality of contacts to the firstand second fingers.
 19. The method of claim 18 , further comprising thestep of coupling the contacts to a printed circuit board.
 20. The methodof claim 19 , further comprising the step of coupling an integratedcircuit package to the contacts.